System and method for determining at least one parameter of at least one rotating member by means of an absolute position signal

ABSTRACT

The invention concerns a system for determining at least one parameter of at least one member ( 1 ) rotating with respect to a fixed structure ( 2 ), comprising, for each rotating member ( 1 ), an assembly comprising a transponder ( 3 ), a coder ( 5 ), an absolute position sensor ( 6 ) and a device ( 4 ) for detecting the parameter or parameters issuing from the transponder ( 3 ); the said system also comprising an activation device ( 7 ) which is connected to each sensor ( 6 ) and to each detection device ( 4 ), the said activation device being able, according to the absolute position of the coder, to activate the detection device ( 4 ) of an assembly when the transponder ( 3 ) of the assembly is in the transmission/reception cone of the communication means of the said detection device.

The invention concerns a system for determining at least one parameter of at least one member rotating with respect to a fixed structure, a method of determining at least one such parameter and a motor vehicle comprising such a system.

The invention applies typically to the determination of at least one parameter such as the pressure, temperature, deformation or wear of a motor vehicle tyre.

To do this, it is known how to use, for each tyre:

-   -   a transponder which is rotationally fixed to the tyre, the said         transponder being able to measure the parameter or parameters;         and     -   a device for detecting the parameter or parameters issuing from         the transponder, the said device being fixed to the chassis of         the vehicle and comprising an antenna able to transmit an         excitation signal to the transponder and to receive the         measurement or measurements.

To allow communication between the transponder and the detection device, the antenna on the latter is positioned close to the area of movement of the transponder, typically in the wheel arch.

Thus, by activating the detection device, it is possible to periodically obtain the value of the parameter or parameters measured by the transponder and to make this value available to a system, for example a safety system on the vehicle, which monitors and/or uses it.

One problem which is posed concerns the establishment of a procedure for activating the detection device which makes it possible to obtain satisfactory communication between the said device and the transponder. This is because, the antenna having a given transmission/reception cone, the activation must be effected when the transponder is situated in this cone.

According to a first solution, it has been proposed to activate the detection device continuously, but this presents several drawbacks. First of all, it gives rise to high electrical consumption, partly unnecessary when the transponder is not situated in the transmission/reception cone. In addition, it acts on the transponder at each rotation, which, under certain running conditions, is unnecessary and, in the case of an active transponder, consumes its battery power unnecessarily.

In order to attempt to limit the electrical consumption, it has been proposed, according to a second solution, to activate the detection device at a fixed frequency. However, this solution also presents several drawbacks. First of all, it does not make it possible to ensure that the transponder is in the transmission/reception cone when the detection device is activated. In particular, for a given activation frequency, there exist speeds of rotation of the transponder for which this condition is not fulfilled, which is incompatible with a use of the parameter or parameters in a safety function for the vehicle. In addition, this solution does not guarantee a determination of the parameter or parameters at a given frequency, for example according to the operating conditions of the vehicle.

In order to attempt to resolve the drawbacks of this second solution, it has been proposed to increase the size of the antenna so as to increase the corresponding transmission/reception cone. However, apart from the fact that this possibility can only limit these drawbacks without completely resolving them since a shadow area in the communication is always present, the increase in the size of the antenna causes increased integration constraints in the wheel arch as well as a higher power and therefore electrical consumption.

To resolve all these drawbacks, the invention proposes in particular a determination system which makes it possible to synchronise communication between the antenna and the transponder when the latter is in the transmission/reception cone, so as to make the communication secure whilst optimising electrical consumption, whilst being able to adapt the communication frequency to operating conditions of the vehicle.

To this end, and according to a first aspect, the invention proposes a system for determining at least one parameter of at least one member rotating with respect to a fixed structure, the said system comprising, for each rotating member, an assembly comprising:

-   -   a transponder rotationally fixed to the rotating member, the         said transponder being able to measure the parameter or         parameters to be determined;     -   a coder rotationally fixed to the rotating member, the said         coder comprising a main track and a rotation pulse track, the         said rotation pulse track comprising a reference singularity         whose angular position is indexed with respect to the angular         position of the transponder on the rotating member;     -   a sensor fixed to the fixed structure, the said sensor being         disposed opposite to and at a reading distance from the coder,         the said sensor comprising an electronic circuit able to deliver         a signal representing the angular position of the coder with         respect to the fixed structure and a rotation pulse signal         comprising a reference pulse corresponding to the detection of         the reference singularity, the said circuit also comprising         means of resetting the coder position signal with respect to the         position of the singularity so as to deliver an absolute         position signal of the said coder with respect to the         singularity;     -   a device for detecting the parameter or parameters issuing from         the transponder, the said device being fixed to the fixed         structure and comprising a communication means able to send an         excitation signal to the transponder and to receive the         measurement or measurements;         the said system also comprising:     -   an activation device which is connected to each sensor and to         each detection device, the said activation device being able,         according to the absolute position of the coder, to activate the         detection device of an assembly when the transponder of the         assembly is in the transmission/reception cone of the         communication means of the said detection device.

According to a second aspect, the invention proposes a method of determining at least one parameter of at least one member rotating with respect to a fixed structure by means of such a system, in which the activation device compares the absolute position of the coder with an activation position and, when the two positions are equal, the said device activates or enables the activation of the detection device.

According to a third aspect, the invention proposes a motor vehicle comprising such a system, each assembly being disposed so as to determine at least one parameter of a tyre of the said vehicle.

Other objects and advantages of the invention will emerge during the following description given with reference to the accompanying drawing, which schematically depicts a vehicle comprising a determination system according to the invention.

The invention concerns a system for determining at least one parameter of at least one rotating member 1 in rotation with respect to a fixed structure 2. According to the embodiment described in relation to the figure, this system is intended for determining at least one parameter of at least one tyre 1 of a motor vehicle. In particular, the system allows the determination of the pressure, the temperature, the deformation and/or the wear of all the tyres 1 on the vehicle.

To do this, the system comprises, for each tyre 1, an assembly comprising a transponder 3 able to measure the parameter or parameters to be determined, and a device 4 for detecting the parameter or parameters issuing from the transponder 3. The transponder 3 is rotationally fixed to the tyre 1 and the detection device 4 is fixed, close to the transponder 3, to the chassis 2 of the vehicle. According to other applications, the transponder 3 can be fixed to the wheel or to the bearing on which the wheel is mounted.

The determination system makes it possible, by activating the detection device 4, to periodically obtain the value of the parameter or parameters measured by the transponder 3 and to make this value available to a system which is fixed with respect to the chassis 2, for example a vehicle safety system, which monitors and/or uses it. In particular, the automatic determination of the parameter or parameters can make it possible to warn the driver in the event of abnormality. In addition, the parameter or parameters can be used in driving aid systems such as wheel anti-locking (ABS), direction control (ESP) or electrical steering assistance (ESA), so as to adapt the action of these systems according to the value of the parameters determined.

An assembly consisting of transponder 3 and detection device 4 is known from the prior art:

-   -   the detection device 4 comprising a communication means, for         example in the form of a directional antenna, able to transmit         an excitation signal, for example RF, to the transponder 3 and         to receive the measurement or measurements; and     -   the transponder 3 being able to be of the active type or of the         passive type depending on whether it is supplied by its own         battery in order to perform the measurement and communication or         whether these functions are induced by the excitation signal         issuing from the detection device 4. For determining the         pressure of the tyre 1, the transponder 3 can be of the surface         acoustic wave (SAW) type.

In the vehicle according to the invention, the antenna is housed in the wheel arch on which the tyre 1 is mounted and the transponder 3 is housed in the valve of the tyre 1. Thus the distance between antenna and transponder 3 is reduced, which makes it possible to optimise the electrical power necessary for the communication of the measurements between the tyre 1 and the chassis 2.

In a variant, it is also possible to provide for the transponder 3 to be disposed in the tread of the tyre 1, in particular in order to measure the deformation and wear thereof. The assembly also comprises a coder 5 rotationally fixed to the tyre 1 and a sensor 6 fixed to the chassis 2 of the vehicle. In particular, the coder 5 and/or the sensor 6 can be disposed at the wheel bearing, as described for example in the document FR-2 700 588 issuing from the applicant. The coder 5 can in particular be rotationally fixed to the rotating race of the bearing and the sensor 6 can be associated with the fixed race or dissociated from it, in order to be opposite to and at a reading distance from the coder 5.

The function of the coder 5 is to deliver information on the angular position of the tyre 1 and reference angular position information. To this end, the coder 5 comprises a main track and a rotation pulse track, the said rotation pulse track comprising a reference singularity which, as will be seen later in the description, is indexed with respect to the angular position of the transponder 3 on the tyre 1.

According to one embodiment, the coder 5 is formed by a magnetic ring comprising on its surface the main track and the rotation pulse track which are concentric, the said tracks comprising a succession of North and South poles, the reference singularity being produced by a magnetic transition which is different from the others.

Opposite to and at a reading distance from this coder 5, the sensor 6 is provided which comprises an electronic circuit able to deliver a signal representing the angular position of the coder 5 with respect to the chassis 2 and a rotation pulse signal comprising a reference pulse corresponding to the detection of the reference singularity. In addition, the electronic circuit comprises means of resetting the position signal of the coder 5 with respect to the position of the singularity, so as to deliver an absolute position signal of the said coder 5 with respect to the singularity, and therefore an absolute position signal of the tyre 1 since the coder 5 is rotationally fixed thereto.

According to one embodiment, the sensor 6 comprises at least three sensitive elements, at least two of which are positioned opposite the main track and at least one of which is positioned opposite the rotation pulse track.

In a particular example, the sensitive elements are chosen from the group comprising Hall effect sensors, magnetoresistors and giant magnetoresistors.

The sensor 6 used in this embodiment is able to deliver two periodic electrical signals S1, S2 in quadrature by means of the sensitive elements disposed opposite the main track and an electrical signal S3 by means of the sensitive elements disposed opposite the rotation pulse track.

The principle of obtaining the signals S1 and S2 from a plurality of aligned sensitive elements is for example described in the document FR-2 792 403 issuing from the applicant.

However, sensors comprising two sensitive elements which are able to deliver the signals S1 and S2 are also known.

From the signals S1, S2 and S3, the electronic circuit is able to deliver square digital position signals A, B in quadrature and a rotation pulse signal C. The signals A, B representing the angular position of the coder but also its speed of rotation as well as its direction of rotation.

A principle of obtaining the digital signals A, B and C and various embodiments of the magnetic singularities are described in the documents FR-2 769 088 and EP-0 871 014.

According to one embodiment, the electronic circuit also comprises an interpolator, for example of the type described in the document FR-2 754 063 issuing from the applicant, making it possible to increase the resolution of the output signals. In particular, a resolution of the angular position of the coder 5 of less than 1° can be obtained.

The sensor 6 can be integrated on a silicon substrate or equivalent, for example AsGa, so as to form an integrated circuit personalised for a specific application, a circuit sometimes termed an ASIC in order to refer to the integrated circuit designed partially or completely according to requirements.

Although the description is given in relation to a magnetic sensor/coder assembly, it is also possible to implement the invention in a similar fashion using a technology of the optical type. For example, the coder 5 can be formed from a metal or glass target on which the main track and rotation pulse track have been etched so as to form an optical pattern similar to the multipole magnetic pattern disclosed above, the sensitive elements then being formed from optical detectors.

The electronic circuit comprises counting means able to determine, from an initial position, the variations in the angular position of the coder 5. In one example embodiment, the counting means comprise a register in which the value of the angular position is incremented or decremented by an angular value corresponding to the number of edges of the signals A and B which are detected, the initial value being for example fixed at zero when the system is commissioned. Thus the processing device makes it possible to know the relative position of the coder 5 with respect to the initial position.

Next, as soon as the reference pulse of the rotation pulse signal is recorded, the electronic circuit makes it possible to reset the relative angular position signal of the coder 5 so as to obtain subsequently and continuously, by virtue of the counting means, the signal on the absolute angular position of the coder 5 with respect to the position of the singularity.

Apart from the assembly or assemblies, the system comprises an activation device 7, in the form of a calculation unit, which is connected to each sensor 6 and to each detection device 4, so as to be able on the one hand to use the absolute position signal and on the other hand to activate each detection device 4 in order to collect the value of the parameter or parameters detected. According to the invention, the activation device 7 is able, according to the absolute position of the coder, to activate the detection device 4 of an assembly when the transponder 3 of the assembly is in the transmission/reception cone of the antenna of the said detection device.

The activation device 7 makes it possible to synchronise the passage of the transponder 3 into the cone with the activation of the detection device 4. This is because, the position of the singularity being indexed with respect to that of the transponder 3, there exists a known constant difference between the absolute position signal and the position of the transponder 3. The angular range of the transmission/reception cone of the antenna being known, this difference is used by the activation device 7 in order to determine an activation position in which the transponder 3 is in the said cone. In particular, the system according to the invention makes it possible, by virtue of the synchronisation, to optimise the life of the battery supplying the activation device 7 and, where applicable, the battery supplying the transponder 3 in the case where the latter is active.

According to one embodiment, each coder 5 comprises means of coding the pulse which are different from one coder 5 to another, the activation device 7 comprising means of identifying the coding so as to activate the detection device 4 of the assembly of the coder 5 from which the pulse came. This embodiment may make it possible to simplify the wiring between the assemblies and the activation device 7, since the recognition of the tyre 1 concerned no longer depends on the physical addressing of the position signals to the activation device 7. In particular, according to this embodiment, it is possible to provide a multiplexed or wireless connection between the assemblies and the activation device 7. Moreover, this embodiment makes it possible to electronically identify the wheel from which the parameter or parameters came.

In one example embodiment, the coding means comprise a number of supplementary singularities which are distributed on the coder 5.

In a determination method using a system according to the invention, the activation device 7 compares the absolute position of the coder 5 with the determined activation position and, when the two positions are equal, the device activates or enables the activation of the detection device 4 so as to allow the detection of the parameter or parameters.

When the activation device 7 enables activation, provision may be made for effecting the said activation at variable interrogation periods which are determined according to the operating conditions of the tyre 1. In particular, these conditions may be a function of the measured parameters (pressure, temperature), the running conditions of the vehicle such as the speed or the state of the road (rain or snow condition for example), or the positioning of the tyre 1 (front or rear).

In one example embodiment, at least one speed threshold can be defined for the vehicle so that:

-   -   below the threshold, the activation is carried out at a         frequency f_(i);     -   above the threshold, the activation is carried out at a         frequency which is a multiple of f_(i).

It may also be decided to determine the pressure of the rear tyres 1 more frequently than that of the front tyres.

To do this, the activation device 7 is also supplied with the pertinent parameters and with the required conditions, the said device comprising means of timing of the activation when the latter is enabled.

According to one embodiment of the determination method, the activation position used can be equal to the indexed position of the transponder 3 with respect to the reference singularity.

According to another embodiment, provision can be made, after possibly the initial use of the indexed position as the activation position, an iterative procedure of optimising the activation position, the said procedure being able to be triggered continuously or periodically.

The optimisation procedure can make provision for analysing the quality of the signal issuing from the detection device 4, for example its signal to noise ratio, the communication error rate or the power communicated. If this quality is below a first threshold, incrementing and/or decrementing the activation position by a given step, for example one degree. Iteratively, the procedure makes it possible, by analysing the quality of the corresponding signal, to increment or decrement the activation position in order to obtain an optimised activation position in which the quality of the signal is at a maximum. This optimised position is used subsequently as a new activation position.

A description is given below of the possible embodiments of the indexing of the transponder 3 with respect to the reference singularity, so that the activation or enabling of the activation of the detection device 4 is effected when the absolute position of the coder is equal to a stored activation position.

According to a first embodiment, the indexed position of the transponder 3 with respect to the reference singularity is previously stored in the activation device 7. For example, this indexing is achieved mechanically in the factory or in a workshop, on a bench able to measure the angular difference between the reference singularity and the transponder 3.

According to a variant of this embodiment, the reference singularity is indexed with respect to all the possible angular positions of the transponder 3 on the tyre 1, these positions each corresponding to a possible position of mounting of the wheel on the vehicle.

In this embodiment, the activation device 7 is able to activate the detection device 4 when each possible angular position of the transponder 3 is in the transmission/reception cone of the antenna. Thus, for example for four possible positions, the detection device 4 will be activated four times, the communication being achieved in a satisfactory fashion solely in one of these positions.

This embodiment makes it possible, in the case of mounting/removal of the wheel, not to have to redo the indexing.

According to a second embodiment, the determination method comprises an a priori procedure of indexing the position of the reference singularity with respect to the angular position of the transponder 3.

This procedure can be carried out by activation at fixed frequency, for example every second, of the detection device 4 and, when the signal measured by the detection device 4 is satisfactory, determination and recording in the activation device 7 of the indexed position which is equal to the absolute position of the coder 5. As in the optimisation procedure, the quality of the signal is analysed in order to judge whether it is satisfactory.

In particular, this procedure can be triggered whenever the determination system is brought into service, before the determination of the parameter or parameters according to the invention.

According to one embodiment of the method, a second signal quality threshold, lower than the first, is used in the activation device 7. Provision can thus be made, if the quality of the signal is lower than the second threshold, to trigger the indexing procedure in place of the optimisation procedure. In particular, this embodiment makes it possible, in the case of cutting off the electrical supply to the system when the parameter or parameters are determined, to initiate an indexing procedure in order to reset the synchronisation. In addition, if the optimisation procedure does not make it possible to converge towards an optimised position, this embodiment also makes it possible to initiate an indexing procedure in the course of optimisation. 

1. A system for determining at least one parameter of at least one member (1) rotating with respect to a fixed structure (2), said system comprising, for each rotating member (1), an assembly comprising: a transponder (3) rotationally fixed to the rotating member (1), the transponder being able to measure the parameter or parameters to be determined; a coder (5) rotationally fixed to the rotating member (1), the coder comprising a main track and a rotation pulse track, the rotation pulse track comprising a reference singularity whose angular position is indexed with respect to the angular position of the transponder (3) on the rotating member (1); a sensor (6) fixed to the fixed structure (2), the sensor being disposed opposite to and at a reading distance from the coder (5), the sensor comprising an electronic circuit able to deliver a signal representing the angular position of the coder (5) with respect to the fixed structure (2) and a rotation pulse signal comprising a reference pulse corresponding to the detection of the reference singularity, the circuit also comprising means or resetting the coder position signal with respect to the position of the singularity so as to deliver an absolute position signal of the said coder (5) with respect to the singularity; a device (4) for detecting the parameter or parameters issuing from the transponder (3), the device being fixed to the fixed structure (2) and comprising a communication means for sending an excitation signal to the transponder (3) and for receiving the measurement or measurements; and an activation device (7) which is connected to each sensor (6) and to each detection device (4), the activation device being able, according to the absolute position of the coder, to activate the detection device (4) of an assembly when the transponder (3) of the assembly is in the transmission/reception cone of the communication means of the detection device.
 2. A system according to claim 1, characterised in that the coder (5) is formed from a magnetic ring comprising on its surface the main track and the rotation pulse track which are concentric, the tracks comprising a succession of s North and South poles, the reference singularity being produced by a magnetic transition which is different from the others.
 3. A system according to claim 1, characterised in that the reference singularity is indexed with respect to all the possible angular positions of the to transponder (3) on the rotating member (1), the activation device (7) being able to activate the detection device (4) when each possible angular position of the transponder (3) is in the transmission/reception cone of the communication means.
 4. A system according to any one of claims 1 to 3, characterised in that each coder (5) also comprises means or coding the pulse which are different from one coder (5) to another, the activation device (7) comprising means or identifying the coding so as to activate the detection device (4) of the assembly of the coder (5) from which the pulse came.
 5. A system according to claim 4, characterised in that the coding means comprise a number of supplementary singularities which are distributed over the coder (5).
 6. A method of determining at least one parameter of at least one member (1) rotating with respect to a fixed structure (2) by a system according to claim 1, in which the activation device (7) compares the absolute position of the coder (5) with an activation position and, when the two positions are equal, the device activates or enables the activation of the detection device (4).
 7. A method according to claim 6, characterised in that the activation position is equal, at least initially, to the indexed position of the transponder (3) with respect to the reference singularity.
 8. A method according to claim 6, characterised in that it comprises an iterative procedure of optimising the activation position in which the quality of the signal issuing from the detection device (4) is analysed, and, if the quality is below a first threshold, the activation position is incremented and/or s decremented by a given step in order to determine a new optimised position which is used subsequently by the activation device (7) as the new activation position.
 9. A method according to any one of claims 6 to 8, characterised in that, when to the activation device (7) enables activation, the latter is effected at variable interrogation periods which are determined as a function of operating conditions of the rotating member (1).
 10. A method according to any one of claims 6 to 8, characterised in that the is indexed position of the transponder (3) with respect to the reference singularity is previously stored in the activation device (7).
 11. A method according to any one of claims 6 to 8, characterised in that it comprises a prior procedure of indexing the position of the reference singularity with respect to the angular position of the transponder (3) on the rotating member (1).
 12. A method according to claim 11, characterised in that the indexing procedure is effected by activation of the detection device (4) at fixed frequency and, when the signal measured by the said device is satisfactory, determination of the indexed position which is equal to the absolute position of the coder (5).
 13. A method according to claim 8, characterized in that it comprises a prior procedure of indexing the position of the reference singularity with respect to the angular position of the transponder (3) on the rotating member (1), in which, if the quality of the signal is below a second threshold which is lower than the first threshold, the indexing procedure is carried out in place of the optimisation procedure.
 14. A motor vehicle comprising a system according to any one of claims 1 to 3, each assembly being disposed so as to determine at least one parameter of a tyre (1) of the vehicle.
 15. A vehicle according to claim 14, characterised in that the communication means is housed in the arch of the wheel on which the tyre (1) is mounted and in that the transponder (3) is housed in the valve of the tyre (1).
 16. A method according to claim 13, characterised in that the indexing procedure is effected by activation of the detection device (4) at fixed frequency and, when the signal measured by the said device is satisfactory, determination of the indexed position which is equal to the absolute position of the coder (5).
 17. A motor vehicle comprising a system according to claim 4, each assembly being disposed so as to determine at least one parameter of a tyre (1) of the vehicle.
 18. A vehicle according to claim 17, characterised in that the communication means is housed in the arch of the wheel on which the tyre (1) is mounted and in that the transponder (3) is housed in the valve of the tyre (1).
 19. A motor vehicle comprising a system according to claim 5, each assembly being disposed so as to determine at least one parameter of a tyre (1) of the vehicle.
 20. A vehicle according to claim 19, characterised in that the communication means is housed in the arch of the wheel on which the tyre (1) is mounted and in that the transponder (3) is housed in the valve of the tyre (1). 